linux-kernel - Re: [RFC PATCH 0/2] apply write hints to select the type of segments

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Date:   Thu, 9 Nov 2017 10:16:24 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     Hyunchul Lee <hyc.lee@...il.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        Hyunchul Lee <cheol.lee@....com>
Subject: Re: [RFC PATCH 0/2] apply write hints to select the type of segments

On 11/09, Chao Yu wrote:
> On 2017/11/9 13:51, Hyunchul Lee wrote:
> > From: Hyunchul Lee <cheol.lee@....com>
> > 
> > Using write hints[1], applications can inform the life time of the data
> > written to devices. and this[2] reported that the write hints patch
> > decreased writes in NAND by 25%.
> > 
> > This hints help F2FS to determine the followings.
> >   1) the segment types where the data will be written.
> >   2) the hints that will be passed down to devices with the data of segments.
> > 
> > This patch set implements the first mapping from write hints to segment types
> > as shown below.
> > 
> >   hints                     segment type
> >   -----                     ------------
> >   WRITE_LIFE_SHORT          CURSEG_COLD_DATA
> >   WRITE_LIFE_EXTREME        CURSEG_HOT_DATA
> >   others                    CURSEG_WARM_DATA
> > 
> > The F2FS poliy for hot/cold seperation has precedence over this hints, And
> > hints are not applied in in-place update.
> 
> Could we change to disable IPU if file/inode write hint is existing?

Well, this is a hint which is not related to IPU. I think user should be aware
of controlling IPU.

> > 
> > Before the second mapping is implemented, write hints are not passed down
> > to devices. Because it is better that the data of a segment have the same 
> > hint.
> > 
> > [1]: c75b1d9421f80f4143e389d2d50ddfc8a28c8c35
> > [2]: https://lwn.net/Articles/726477/
> 
> Could you write a patch to support passing write hint to block layer for
> buffered writes as below commit:
> 0127251c45ae ("ext4: add support for passing in write hints for buffered writes")
> 
> Thanks,
> 
> > 
> > Hyunchul Lee (2):
> >   f2fs: apply write hints to select the type of segments for buffered
> >     write
> >   f2fs: apply write hints to select the type of segment for direct write
> > 
> >  fs/f2fs/data.c    | 101 ++++++++++++++++++++++++++++++++----------------------
> >  fs/f2fs/f2fs.h    |   1 +
> >  fs/f2fs/segment.c |  14 +++++++-
> >  3 files changed, 74 insertions(+), 42 deletions(-)
> >